In this project we are coupling genetic study of selected families and twin pairs with epidemiologic, immunologic, serologic and neurochemical studies of disorders due to multiple factors such as multiple sclerosis and Parkinsonism. This approach should clarify the etiology of these diseases, indicate individuals or populations at high risk and suggest mechanisms for prevention and treatment. To date, 18 presumptive "Multiple Sclerosis" families and 97 twin pairs with this condition have been ascertained. Over 15 twin pairs with Parkinsonism have been ascertained.